Thread: Troubleshooting ideas please

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Ok long story short,have been at Hot August nights the last few days and spiked my ignition box on Wednesday.Replaced the Mallory Hyfire 4C with a Mallory 6AL ignition system and fired right up after instalation.Idles and starts fine but as I accelerate it will missfire on some cylinders.Still drives no problem but I can hear the misfire in all rpm ranges.Plugs, leads cap and rotor are all new and the distributor module(distributor is a mag pickup) is working fine.The only thing I have not checked in the ignition system is the coil,could this be failing and when a spike occurs can this affect the coil.The reason I am looking at the electrical side is because of the spike obviously,but is there somewhere else I am missing.Thanks for any input.

Really like the Willys truck! I believe that the coil breaking down under load is a good possibility for your miss. Also, are you confident in your plugs? There seem to be more and more cases of faulty plugs out of the box these days with assembly done in far east shops.

how did you spike the box? did you try another coil ? all wires and grounds good? did you try to run it with the tack un hooked alot of the hi speed missing i worked on was bad new plugs or to much end gap .i have seen were spark will walk around the dist cap in the dark from bad plugs that were on to new 4.3s in a sea ray after another guy put new boxs and wires in there was a bad run on AC plugs after that boat i was pulling plugs left and right

The 6AL box with a MSD Blaster coil puts out a mega spark! It will fire spark plugs with the ground electrodes burnt completely off the plugs without even missing a beat. But, if the spark plug wires, or the cap and rotor are not in great condition this large spark will find the path of least resistance. Look inside the cap for carbon tracking.

Make sure you don't have the 3000 RPM test chip installed.

it is not a 6al msd or blaster coil . it a mallory not the same animal. they have dip switchs? some did.. i have had customers use there stuff . i allways use MSD stuff so i can not tell you if the tac can short out the box but it could on some .the thunder boxs put out good power to but when AC had so much shift on the plug they rim fired . the wires just would not hold the juice and they would break up

Appreciate all the possible issues,and I will try and get back to you guys as soon as possible.It is driveable and will be driving her home tomorrow after having a great week in Reno and will then do more diagnosing.This whole issue started when my electric fan wiring shorted and I got a quick spike that I noticed on my voltmeter while driving and that was it,dead Willys.Troubleshooted to the old ignition and with new one installed fired right up and off I went but with a slight misfire through the rpm range under load and also cruising.I am a little suspect of the plugs also and will have to take a closer look as they were replaced(Accel 0574S).The only thing I haven't really looked at is the coil which I am not sure how to check to see if it is the culprit.The cap looks good with no visible arcing and new plug leads.Will also try the tac un hooked.Thanks again for the advice.

Thought I would just let those that responded that all is well.It appears that faulty new plugs was the issue.Can't believe that you cannot rely on new plugs out of the box.Now I have a bunch of plugs that I will have to use with trial and error to make sure they are useable.

OK bad plugs was new to me at the boat yard 20 years ago i had alot of bad plugs in new boats .it costed the boat yard to new thunder bolt boxs and two sets of wire as they could not send back good parts $$$$ before i looked at the start of the missing still i will not use a AC plug